Symmetrical bipolar transistors have many applications. In a known application, a bipolar transistor is used as a reverse-polarity protection element in a coupling circuit to a bus system. (See European Patent Publication No. EP-A-0487 759, FIG. 3.) Such reverse-polarity protection is preferably suitable for assemblies in bus systems, in computers and in controllers with a storage capability. The reverse-polarity protection element is located in a signal coupling path and serves as a controllable element which switches the signal coupling path on and off as a function of the polarity of an electrical signal. The known bipolar transistor is designed as a double-emitter transistor whose emitter current can be controlled uniformly in both directions.
A bipolar transistor structure is also generally suitable for checking whether a potential difference is less than a specific value and thus, in addition, whether a voltage is approaching another voltage. Until now, comparators have been used for such applications. The required comparator arrangements are normally rather complex, however. A national German application having an older priority (German Patent Application No. DE-A-43 16 608) discusses a bipolar transistor structure.
If a bipolar transistor structure is intended to be integrated in an integrated circuit, it is desirable to minimize the power losses which occur and to keep the currents for driving such bipolar transistor structures correspondingly low. The object of the present invention is to find a driver circuit for a symmetrical bipolar transistor and for a bipolar transistor structure in an IC circuit, which operates with drive currents which are as low as possible.